1. Field of the Invention
The present invention relates to a check valve assembly for an endoscope. More particularly, the present invention relates to a check valve assembly for use between an endoscope and a fluid supply source, and in which a valve element can open and close reliably for preventing backflow even in a simple structure.
2. Description Related to the Prior Art
An endoscope includes an elongated tube or guide tube and a fluid lumen for water jet. The elongated tube is entered in a body cavity of a patient for imaging. The fluid lumen extends through the elongated tube, and used for ejecting fluid through a water jet nozzle at a distal end of the elongated tube. Examples of the fluid include drug solution for treatment, washing water such as physiological saline water, and the like. A fluid supply source or fluid dispensing apparatus is connected with the fluid lumen of the endoscope, and introduces the fluid by use of a supply pump. A check valve assembly for preventing backflow is used between the endoscope and the fluid supply source, and operates for preventing a backflow of the fluid from the fluid lumen back into the fluid supply source.
The fluid lumen of the endoscope has a distal end and a proximal end. The distal end has a water jet nozzle disposed at a distal surface of the elongated tube. The proximal end has a fluid port for water jet by connection with the check valve assembly. The fluid port is formed with a handle device of the endoscope on a proximal side of the elongated tube. Also, it is possible that the fluid port is formed with a connector disposed with the handle device for connection with a universal cable.
U.S. Pat. No. 6,569,087 (corresponding to JP-B 3488170) discloses an adapter tube set having first and second connection couplings at its ends. The first connection coupling is coupled to the fluid port of the endoscope. The second connection coupling is coupled to the fluid supply source. The check valve assembly is incorporated in the second connection coupling. The check valve assembly includes a discharge nozzle unit (or valve seat device) and an elastic valve sleeve (or elastic tubular portion or elastic check valve flap). The discharge nozzle unit has a cylindrical wall and plural fluid openings formed in the wall. The elastic valve sleeve covers the outside of the discharge nozzle unit. The elastic valve sleeve when in a normal state closes the fluid openings by tight contact with the outside of the discharge nozzle unit, and blocks supply of the fluid. When the fluid flows abruptly into the discharge nozzle unit, fluid pressure of the fluid from the fluid openings presses open the elastic valve sleeve to allow the fluid to flow into the fluid lumen. When the fluid pressure applied to the inside of the elastic valve sleeve decreases, return force of the elastic valve sleeve recovers its original form with the normal diameter. A backflow of the fluid can be prevented by closing of the fluid openings with the elastic valve sleeve.
The elastic valve sleeve constituting the check valve assembly has an inner diameter constant for the purpose of tight contact with the discharge nozzle unit in a normal state. Also, the elastic valve sleeve has a small diameter portion and a large diameter portion. The small diameter portion has a smaller diameter for a position to cover the fluid openings. The large diameter portion has a larger diameter than the small diameter portion. The large diameter portion is squeezed fixedly between the discharge nozzle unit and a valve housing in the axial direction, the discharge nozzle unit being mounted in the valve housing. Thus, the large diameter portion of the elastic valve sleeve with a larger thickness always contacts the discharge nozzle unit tightly. The small diameter portion with a smaller thickness is pressed open by the fluid pressure.
However, the elastic valve sleeve according to U.S. Pat. No. 6,569,087 (corresponding to JP-B 3488170) has a specific shape including the small diameter portion and the large diameter portion and must be formed only by use of particular molds or the like. This increases a manufacturing cost. It is conceivable to use a rubber tube of a commercially available type for the check valve assembly. If the check valve assembly is constituted by the rubber tube and the discharge nozzle unit of U.S. Pat. No. 6,569,087 (corresponding to JP-B 3488170), it is impossible exactly to position the check valve assembly for a position of the fluid openings typically when the return force of the rubber tube is too small.
If the rubber tube with a normally small diameter is used to increase return force in a state covering the discharge nozzle unit, the rubber tube tightly contacts the discharge nozzle unit with an equal level of the return force at any of its portions. The check valve assembly does not function, because a portion of the fluid openings cannot be controlled locally for opening and closing.